Subcutaneous delivery devices using a cannula are effective for many applications. However, the pain normally induced by the cannula has prompted the development of less painful delivery methods. Recently, a number of intradermal devices employing microneedles have been designed. The microneedles have a length selected to penetrate the skin to a depth where a drug or pharmaceutical agent can be delivered to a patient.
In humans, the skin is made up of several layers, with the upper composite layer being the epithelial layer. The outermost layer of the skin, the stratum corneum, has well known barrier properties to prevent molecules and various substances from entering the body and analytes from exiting the body. Bouwstra, et al., (2001) Skin Pharmacol Appl Skin Physiol, 14 Suppl 1:52–62.
The stratum corneum is a complex structure of compacted keratinized cell remnants having a thickness of about 10–30 microns which forms a waterproof membrane to protect the body from invasion by various substances and from the outward migration of various compounds.
The natural impermeability of the stratum corneum prevents the administration of most pharmaceutical agents and other substances through the skin. Numerous methods and devices have been proposed to enhance the permeability of the skin and to increase the diffusion of various drugs through the skin to be utilized by the body. Typically, increasing either the permeability of the skin or the force or energy used to drive therapeutics through the skin enhances delivery of drugs through the skin. Bouwstra, et al., supra.
Another method of delivering various substances through the skin is by forming micropores or microcuts through the stratum corneum. By penetrating or piercing the stratum corneum and delivering a drug to the skin in or below the stratum corneum, many drugs can be administered effectively. The devices for piercing the stratum corneum generally include a plurality of micron-sized needles or blades having a length selected to pierce the stratum corneum without passing completely through the epidermis. Examples of these devices are disclosed in U.S. Pat. No. 5,879,326 to Godshall et al., U.S. Pat. No. 5,250,023 to Lee et al., and WO 97/48440.
The above-noted devices that include micron-sized needles or blades deliver the substances to the body by allowing the substances to flow through pores or channels in the device. Many of these prior devices do not provide a controlled delivery of a substance to the patient.
The prior methods and devices for the intradermal administration of substances have exhibited limited success. Accordingly, a continuing need exists for an improved device for administration of various drugs and other substances to the body.